Computer graphics software and technology is used to creates visual images from digital data. Images may be created in two dimensions (2-D) or, alternatively, images may be generated from object models defined in three dimensions (3-D).
Two dimensional images may be created and stored as either resolution-dependent raster images or as resolution-independent vector images. Raster images are composed of a predetermined number of picture elements (pixels). The level of detail in a raster image is determined by the number of pixels in the image and is therefore limited when the image is created. Alternatively, two dimensional images may be stored as vector images. Vector images are created and stored as resolution-independent mathematically defined lines and curves. Prior to printing or display, a 2-D rendering process converts the mathematically defined lines and curves to pixels. Vector image 2-D rendering may be accomplished by software in the computer system or may be accomplished by software residing in the display device, such as by a PostScript.TM. interpreter in a laser printer.
Three dimensional models may also be used to create graphic images. Three dimensional resolution-dependent models may be created using a 3-D array of discrete volume elements known as voxels. The level of detail in a voxel based 3-D model is determined by the number of discrete voxel elements and generally cannot be increased. Voxel based 3-D models are not further addressed in this disclosure.
Three dimensional models may also be created in a resolution-independent format. Resolution-independent 3-D models may be stored as parametric surfaces mathematically defined on x, y, and z axes, alternatively, polygon based surface models in which modeled object surfaces are approximated by many small polygonal facets may be used, still other modeling alternatives include, for example, non polygon-based models as well as alternative coordinate systems, such as polar coordinate systems.
To print or display a 3-D model, a 3-D rendering process is used to create a 2-D view of 3-D object surfaces as if the object were being viewed from a particular point in 3-D space. The 3-D rendering process may be either resolution-dependent or resolution-independent. Resolution-dependent rendering produces a 2-D view having a fixed number of pixels. Resolution-dependent 3-D rendering is described in, for example, Foley, et al., Computer Graphics: Principles and Practice, 2nd ed., Addison Wesley Publishing company, 1990, ISBN 0-201-12110-7. Alternatively, 3-D rendering may be resolution-independent. Resolution-independent 3-D rendering produces a 2-D vector image view of the modeled object. A 2-D rendering process is subsequently used to enable printing or display of the produced 2-D vector image. Resolution independent 3-D rendering is provided by software products such as Adobe Dimensions 2.0.TM. and is described in U.S. Pat. No. 5,544,291 entitled Resolution-Independent Method For Displaying a Three Dimensional Model in Two-Dimensional Display Space.
During 3-D rendering, details may be added to rendered 3-D model surfaces by use of image mapping techniques. Mapping of 2-D raster images to 3-D object surfaces during resolution dependent 3-D rendering is known and described by, for example, Foley, et al. Similarly, mapping of 2-D vector images to 3-D object surfaces during resolution-independent 3-D rendering is known and is provided by, for example, Adobe Dimensions 2.0.TM. software. Graphic image creation would be further aided by computer graphics systems allowing precise mapping of 2-D raster images to resolution-independent 3-D renderings.